1. Field of the Invention
This invention relates to the field of medical imaging and particularly to a hybrid imaging method and apparatus used to monitor and optimize the placement of interventional medical devices in human tissues.
2. Background of the Art
A number of techniques, methodologies, apparatus and systems have been proposed to improve the accuracy of instrumentality placement such as needle or catheter placement into tissue based on measurements from 3D imaging formats. These imaging formats (such as Magnetic Resonance Imaging, sonographs (ultrasound), fluoroscopy, X-ray, and the like) locate the needle entry device in relation to treatment- or therapy-targeted tissue, such as MR-detected target tissue. These imaging formats generate imaging data that are used to determine the appropriate positioning of the needle during treatment, which needle typically is placed in a guide device and moved into the tissue. In many cases, the needle is delivered solely on the basis of this imaging data information and confirmation of the final needle position relative to the target requires a second set of images to be acquired. In cases where tissue stiffness variations are extreme, the needle may deviate from the desired path and deflect on-route to the target tissue. Similarly, the needle may distort the tissue itself and thereby move the target tissue to a new location, such that the original targeting coordinates are no longer correct. Further limitations of current systems include the fact that needle position is often determined by reference to its artifact generated in the MR images. From this artifact, the operator infers the actual needle position relative to the target position. In many situations this is appropriate; however, when targeting small lesions (i.e. <7 mm), the needle artifact (often 5-9 mm) may obscure the target, limiting the ability to use even real-time imaging data, as from MRI, to validate needle/target position.
Numerous articles have been published in the medical literature describing imaging methods which can be used to monitor and optimize the placement of interventional medical devices in human tissues (e.g., Greenman et al, Magnetic Resonance in Medicine, vol. 39:108-115, 1998; Orel et al., Radiology. vol. 193, pp. 97-102, 1994; Kuhl et al., Radiology. vol. 204, pp. 667-675, 1997; Fischer et al., Radiology, vol. 192, pp. 272-272, 1994; Doler et al., Radiology, vol. 200, pp.863-864, 1996; Fischer et al., Radiology, vol. 195, pp. 533-538, 1995; Daniel et al., Radiology, vol. 207, pp. 455-46, 1998; Heywang-Kobrunner et al., European Radiology, vol. 9, pp. 1656-1665, 1999; Liney et al., Journal of Magnetic Resonance Imaging, vol. 12, pp. 984-990, 2000; Schneider et al., Journal of Magnetic Resonance Imaging, vol. 14, pp. 243-253, 2001; Sittek et al., Der Radiologe, vol. 37, no. 9, pp 685-691, 1999; Jolesz, Journal of Magnetic Resonance Imaging, vol. 8, pp. 3-6, 1998; Lufkin et al., Radiology, vol. 197, pp. 16-18, 1995; Silverman et al., Radiology, vol. 197, pp. 175-181, 1995; Kaiser et al., Investigative Radiology, vol 35, no. 8, pp. 513-519, 2000; Tsekos et al., Proceedings of the IEEE 2nd International Symposium on Bioinformatics and Bioengineering Conference, 2001, pp. 201-208).
To address limitations described in the published prior art, a means to verify the actual trajectory of the needle is needed. A satisfactory method must be capable of observing the target tissue to ensure either that needle deflection or target tissue movements can be incorporated into the needle delivery path, thereby ensuring accurate needle delivery. Modified bore design MR magnet systems have been developed to provide more open access to the patient. As such, imaging and needle manipulation can take place concurrently with the physician having some access to the patient while the patient is positioned in the bore. However, these “open” systems are not always available and are often of suboptimal field strength, which can result in reduced image quality. Other proposed solutions in the art involve in-bore robotic devices that enable manipulation of the needle within the bore of the imaging magnet. While this approach usefully addresses the issues of tissue/needle deflection, it also removes the normally close interaction between the radiologist and patient, which may lead to high levels of patient anxiety.